Surgical intervention may require the manipulation of one or more medical devices in close proximity to a nerve or nerves, which may risk damage to the nerve tissue. For example, medical devices may be used to cut, extract, suture, coagulate, or otherwise manipulate tissue including tissue near or adjacent to neural tissue. Spinal decompressions, which may be preformed to remove tissue that is impinging on a spinal nerve is another such example. It would therefore be beneficial to precisely determine the location and/or orientation of neural tissue when performing a medical procedure to prevent damage to the neural tissue.
For example, knowing the location or orientation of a nerve in relation to a medical device (e.g., a probe, retractor, scalpel, etc.) would enable more accurate medical procedures, and may prevent unnecessary damage to nearby nerves. Although systems for monitoring neural tissue have been described, these systems are typically imprecise. Further, many of these systems require large current densities (which may also damage tissue) and may be severely limited in their ability to accurately guide surgical procedures. For example, in many such systems a current is applied from an electrode (e.g., a needle electrode) in order to evoke an efferent muscular response such as a twitch or EMG response. Such systems typically broadcast, via the applied current, from the electrode and the current passes through nearby tissue until it is sufficiently near a nerve that the current density is adequate to depolarize the nerve.
Because the conductance of biological tissue may vary between individuals, over time in the same individual, and within different tissue regions of the same individual, it has been particularly difficult to predictably regulate the applied current. Furthermore, the broadcast fields generated by such systems are typically limited in their ability to spatially resolve nerve location and/or orientation with respect to the medical device.
For example, U.S. patent application 2005/0075578 to Gharib et. al. and US 2005/0182454 to Gharib et al. describe a system and related methods to determine nerve proximity and nerve direction. Similarly, U.S. Pat. No. 6,564,078 to Marino et al. describes a nerve surveillance cannula system and U.S. 2007/016097 to Farquhar et al. describes a system and method for determining nerve proximity and direction. These devices generally apply electrical current to send current into the tissue and thereby depolarize nearby nerves. Although multiple electrodes may be used to stimulate the tissue, the devices, systems and methods described are do not substantially control the broadcast field. Thus, these systems may be limited by the amount of current applied, and the region over which they can detect nerves.
In addition, many surgical manipulations, particularly spinal decompressions, must be performed in difficult to reach regions, and the surgical procedures performed may necessarily need to navigate narrow and tortuous pathways. Thus, it would be of particular interest to provide devices that are extremely low profile, and/or are adapted for use with existing low-profile surgical devices and systems. Furthermore, it would be of particular interest to provide extremely low profile devices that are flexible and can be moved toward and away from a nerve or nerve root to increase their ability to spatially resolve nerve location and/or orientation with respect to the medical device.
Described herein are devices, systems and methods that may address many of the problems and identified needs described above.